Experimental determination of maximum effective hydrodynamic stress in multiphase flow using shear sensitive aggregates

Abstract

10Maximum effective hydrodynamic stress, max τ , responsible for the breakup of aggregates with size comparable to Kolmogorov eddies, was experimentally determined in an aerated stirred tank. The proposed method is based on the measurement of the maximum stable aggregates size consisting of poly(methyl methacrylate) nanoparticles. The fractal aggregates were broken under various operating conditions in an aerated stirred tank and calibrated with 15 known flow conditions using contracting nozzles to convert the measured aggregate sizes into hydrodynamic stress. It was found that max τ can vary substantially among studied conditions and its magnitude depends on the controlling mechanism including gas jet during bubble formation, bubble rise, bubble burst at the gas-liquid interface or the turbulence generated by the impeller. The measured values are in good agreement with literature data which supports 20 the applicability of this method to characterize the maximum effective hydrodynamic stress in complicated multiphase flow.

High-density mammalian cell cultures in stirred-tank bioreactor without external pH control

“…One possible cause of the observed viability difference could be the cell damage from microbubble bursting at air-liquid interface. Decrease in bubble diameter during bubble bursting has been shown to correlate to rapid increase in maximum effective hydrodynamic stress (Boulton-Stone and Blake, 1993;Chisti, 2000;Nienow, 2006;Villiger et al, 2015). Besides viability, cell culture performance was comparable except the pCO 2 and pH profiles.…”

Establishment of a CFD‐based kLa model in microtiter plates to support CHO cell culture scale‐up during clone selection

“…The cells that were not selected in shaken conditions reacted with impaired growth, which indicated that shear rates might be the reason for the difference in performance. This could be investigated by measuring the hydrodynamic stress directly …”

Study of the Shear-Thinning Effect between Polymer Nanoparticle Surfaces during Shear-Induced Aggregation

“…Furthermore, d f values are increasing with increasing the applied shear rate where for the highest values of 2 for corresponding shear rate values). 19,20,24,39,42 In contrast, the values of d f measured by Ehrl et al 19 for PS NPs are independent of the applied shear rate and equal to 2.63 (Figure 5d). To confirm the low values of d f of about 2.4, an independent analysis of the mass fractal dimension was performed by image analysis.…”

“…Such low values are significantly below a typical value measured for aggregates prepared under shear driven conditions covering the range from 2.5 to 2.8. 19,20,24,39,42 This is a further indication that the soft shell of used core−shell particles has a significant impact on the morphology of formed aggregates and thus their strength.…”

“…Typical values for open aggregates prepared under questioned conditions are between 1.7 and 2.1, 40,41 referring to fully destabilized or partially stabilized conditions, respectively, while values in the range from 2.5−2.8 are typically found for the shear driven aggregation process. 19,20,24,39,42 In Figure 5 is presented the comparison of the measured S(q) as a function of q•⟨R g ⟩ plotted for three different operating temperatures (5, 10, and 25 °C) using core−shell primary particles. For comparison, we also show data measured by Ehrl et al 19 for aggregates composed of polystyrene nanoparticles (PS NPs) with a diameter of 120 nm aggregated at 25 °C using comparable values of the vessel averaged shear rates.…”